Impact resistant inorganic composites

ABSTRACT

An impact resistant composite consisting essentially of metal coated glass fibers in a matrix of glass or ceramics.

United States Patent 11 1 1111 3,869,335

Siefert 1 Mar. 4, 1975 1 IMPACT RESISTANT INORGANIC [56] ReferencesCited COMPOSITES UNITED STATES PATENTS [76] Inventor: August C. Siefert,Goose Ln., 2,693,668 1l/1954 Slayter 161/170 Granville, Ohio 430232,900,274 8/1959 Whitehurst... 117/126 GM 2,940,886 6/1960 Nachtman117/126 GM [2 Filed: g- 9, 1972 2,976,177 3/1961 Warthen 117/114 c3,019,515 2/1962 Whitehurst et a1.. 117/126 GM [211 278905 3,575,7894/1971 Siefert et a1. 161/170 Related U.S. Application Data 3,681,1878/1972 Bou en et a1. 161/170 [60] Division of Set 120,932 March 4, 1971,Pat 3,758,329 9/1973 Garlck 117/126 GM No. 3,702,240, which is acontinuation-impart of Ser. No. 820,015, April 28, 1969, abandoned,Primary E.\'aminer--George F. Lesmes Assistant Examiner-Charles E.Lipsey [52] us. Cl 161/143, 65/3, 65/4, Attorney, Ag nt, or mCarl a n;hn

65/33, 117/70 A, 117/71 R, 117/126 GM, Overman; ll m Hi k y 161/404,161/411 [57] ABSTRACT [5 III. CI. An impact resistant compositeconsisting essential), of [58] g f final coated glass fibers in a matrixof glass or ceram- 9 Claims, 1 Drawing Figure IMPACT RESISTANT INORGANICCOMPOSITES CROSS REFERENCE TO RELATED APPLICATION This is a division ofapplication Ser. No. 120,932, filed Mar. 4, 1971, now US. Pat. No.3,702,240, which in turn is a continuation in part of copendingapplication Ser. No. 820,015 filed Apr. 28, 1969, and now abandoned.

BACKGROUND OF THE INVENTION Glasses and ceramics, even though strong incompression are deficient as structural materials because theyaresubject to catastrophic failure when placed under tension, particularlywhen notched. Attempts have been made to reinforce glasses and ceramicswith fibers of metals, graphite, etc., as for example metal wirereinforced window glass. These attempts, however, have not changed thebasic behavior of the glass or ceramic. The prior art fiber reinforcedglasses and ceramics are brittle in nature, and cannot be bent orimpacted withoutpropagating a crack across a large part of the article.

SUMMARY OF THE INVENTION It has been found that a composite comprisingglass fibers and a glass or ceramic matrix can be formed which will notundergo catastrophic failure provided the fibers are generallyparallelly oriented and a thin layer of a material, such as a metal thatdoes not fuse with the matrix, is interpositioned between the glassfibers and the matrix. This combination can be made in various ways, themost convenient of which involves the step of coating the glass fiberswith a thin coating ofa metal prior to being incorporated in the matrixmaterial. In some instances, the metal coating on the fibers may beoxidized during processing, and in these instances, the metal coatedglass fibers are preferably sheathed in a thin coating of glass prior toincorporation in the glass matrix forming material. The glass sheathingwhich surrounds the metal coating on the fibers prevents oxidationduring fusion of the matrix forming material to insure the presence ofthe metal in the heat integrated composite. It has been found that theglass sheathing can be very thin and still prevent excessive oxidationof the metal coating, and that a low melting point glass can be used forthe sheathing without materially affecting the strength of thecomposite. The glass sheathing in some instances may retain its identityin the composite, and in either instances it may diffuse into the matrixwithout materially reducing the melting temperature of the matrix ofotherwise changing desirable properties of the matrix. It has beenfound, that while some metal coatings must be protected by the glasssheathing, coating of other metals can be incorporated into a glassmatrix without sheathing. The glass fiber ceramic matrix composites ofthe invention do not undergo catastrophic failure when subjected tosharp blows which would shatter or break any known bulk glass material.What is more, many of the embodiments can be deformed with a ball-peenhammer. Although the fibers and the matrix may fracturc slightly at thepoint of impact the fractures do not propagate and are confined to asmall localized portion of the article. Thus the entire article does notbreak. Still other embodiments of the invention, have moduli which donot decrease appreciably and in some instances actually increase withincreasing temperatures, whereas the moduli of metals decrease rapidlyat elevated temperatures. In addition, the composites of the presentinvention are of light weight, since glass has a density ofapproximately 2.2, so that the composites of the present invention havea higher strength to weight ratio, particularly at temperatures at whichaluminum and other metals lose strength rapidly.

The principal object of the present invention is the provision of a newand improved light weight, high strength composite comprising a glassmatrix reinforced with glass fibers and which will not undergocatastrophic failure when subjected to shock.

A further object of the invention is the provision of a new and improvedprocess of making ceramic composites reinforced by metal coated glassfibers, and the metal coatings of which are protected from oxidationeither from the glass, or from the atmosphere.

Further objects and advantages of the invention will become apparent tothose skilled in the art to which it relates from the followingdescriptions of several preferred embodiments hereinafter described.

BRIEF DESCRIPTION OF THE DRAWINGS The solitary FIGURE of the drawing isa photomicrograph of a cross section of the composite of Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE I Silica fibers 0.004inch in diameter were made by feeding a 4 millimeter diameter fusedsilica rod of 99.9 percent purity into an oxygen acetylene flame. Themolten silica produced by the flame is drawn downwardly at a rate of1,000 feet per minute through a slot in a metal coating applicator tubecontaining a A inch depth of molten metal, then past a nitrogenquenching jet and is then wrapped upon a winding drum. The molten metalthat is fed to the drawn silica fiber comprises 99.99 percent aluminumand 0.01 percent bismuth, and is fed to the fiber at approximately 5percent above its melting point. The molten metal is fed to the fusedsilica fiber through an alundum tube having a 0.064 I.D. chamber andwhich is slotted to allow the fiber when positioned in the slot to passthrough molten metal in the chamber. The finished coated fiber has adiameter of 0.0055 inches, and a traverse mechanism causes the fibers tobe bound uniformly upon the drum. The fibers so produced have a tensilestrength of 813,000 pounds per square inch based on the silica fiberdiameter. The aluminum coating was 0.00075 inch thick.

The aluminum coated silica fibers produced as above described areprocessed into a glass matrix composite by pulling a bundle of thecoated fibers through a molten glass bath into a carbon tube. The moltenglass bath was maintained at 950F and had the following compositionbyweight: SiO 4.0; A1 0 3.0; B 0 10.0; PbO, 83.0. The fibers were drawninto the tube for approximately a 4 inch length. After being pulled intothe tube, the tube was allowed to cool to room temperature, and theouter carbon tube was broken away to leave a rod 0.25 inch in diameterand 4 inches long. The rod had a percent by volume loading of thealuminum coated silica fibers distributed uniformly in a generallyparallel arrangement throughout 4-0 percent by volume of the lead glass.The rod had an overall glass content of 80 percent by volume, analuminum content of 20 percent by volume, and had a flexural strength of80,000 pounds per square inch. A specimen when notched had a flexuralstrength of 66,500 pounds per square inch. The rod is surprisinglyductile, and is permanently deformed during bending. The rods do notundergo catastrophic failure, which is surprising for a glass fiberreinforced glass material. When in the form of a glass, the material hasa Youngs Modulus of 8.0 X pounds per square inch, a density of 6.1 gramsper cubic centimeter, a softening point of 400C, and a coefficient ofthermal expansion of 80 X l0' /C. When the material is held at atemperature of 1,000F for approximately one hour, it undergoesdevitrification, and its softening point and strength at hightemperature increase significantly. The solitary figure of the drawingis a photomicrograph of a cross section of the rod produced as abovedescribed.

The photomicrograph clearly shows enlarged sections of glass matrixmaterial spaced from other enlarged sections of matrix material by thininterconnecting sections of matrix material which pass between the metalcoatings of adjacent fibers. The exact reason for the apparent ductilityand lack of catastrophic failure is not known, but it is believed thatcrack propagation, as by shock wave, is stopped by the absorption of theshock waves by the resilient metal coatings which bound the thinconnecting portions of the matrix glass. The groupings of fiberstherefore prevent cracks from propagating throughout the composite, andthe cracks, are limited to the enlarged sections. Cracks in the enlargedsections are staggered relative to each other. The bond strength of thematrix glass with the metal coatings is so great that shear from oneenlarged section of matrix glass that is located between cracks istransferred onto the fibers and then back onto the matrix glass on theopposite side ofa crack. The above explanation is believed to accountfor the ductility and lack of catastrophic failure which the compositesof the invention exhibit.

EXAMPLE 2 A composite is produced using the aluminum coated fibers ofExample 1 by fusion ofa minus 100 mesh powdered glass having thefollowing composition around the fibers: SiO 28.7%; Na O, 11.7%; CaO, 9.1%; BaO, 17.2%; B 0 26.3%; ZnO, 5.3%; and F 3.1%. Twenty percent of thealuminum coated silica fibers are mixed with 50 percent by weight of thepowdered glass with the fibers being oriented in a generally parallelmanner. The mixture is placed between two sheets of stainless steelfoil, the edges of which are bent over to form an envelope. The envelopeis then placed in a furnace and heated to 1,150F while subjected to apressure of approximately psi. The composite produced has substantiallythe same properties at room temperature as that given inExample 1, andthe rod is surprisingly ductile, and undergoes permanent deformation,when bent.

EXAMPLE 3 A composite is produced using the aluminum coated fibers ofExample 1 and having combined therewith fibers having the followingcomposition: SiO 28.7%; Na O, 11.7%; CaO, 9.1%; BaO, 17.2%; B 0 26.3%;ZnO, 5.3%; and P 3.1%. Twenty percent of the aluminum coated silicafibers are mixed with percent by EXAMPLE 4 An aluminum coated fiber ofExample 1 is fed downwardly through a glass tube having an internaldiameter of 4'millimeters and an outside diameter of 6 millimeters. Thebottom /a inch of the tube is' fused by an oxygen-acetylene flame aroundthe aluminum coated silica fiber, and the aluminum coated silica fiberin the fused glass envelope is pulled downwardly through air and wrappedaround a drum. During passage through the air, the fused glass coatingsolidifies into a surface coating of approximately 0.001 inch thick. Theglass tubes and coating have the same composition as the matrix glass ofExample 2. The double coated silica fibers thus produced are groupedtogether in a generally parallel manner and placed between two sheets ofstainless steel foil. The stainless steel envelope thus formed with itscontents are placed in a furnace and heated to 1,150F under a pressureof approximately 15 pounds per square inch. At this temperature, theglass coating fuses together to form a composite having the propertiesof that produced in Example 2.

EXAMPLE 5 Glass fibers of 0.004 inch in diameter are produced from smallstreams of molten glass that are allowed to flow through openings in thebottom of a glass melter, and which streams are attenuated and wrappedupon a winding drum. The glass has the following composition by weight:SiO 65; A1 0 24.7; Na O, 0.3; MgO, 10. This glass has a softening pointof approximately 1,800F. The fibers after solidification are coated withaluminum using the procedure given in US. Pat. No. 2,976,177. Thealuminum coated glass fibers thus produced are then given a coating of aglass using the procedure given in Example 4. The glass coated, aluminumcoated glass fibers thus produced are formed into a composite using theprocedure of Example 4, and the composite thus formed has substantiallythe same properties.

EXAMPLE 6 The process of Example 5 is repeated excepting that theuncoated glass fibers have the following composition by weight: SiO 54;A1 0 l5; Na O, 0.5; TiO 0.05; B 0 8; MgO, 4; CaO, 17.7; and F 0.3. Theglass has a softening point of 1,1 12F, and the coated fibers are formedinto a composite using the procedure of Example 4, at a compositeforming temperature of 1,150F. The composite so produced has the samegeneral flexural properties as does the composite of Example 4, and isuseful at higher temperatures, than is the composite of Example 4.

It will now be apparent that metal coated glass fibers can be used toreinforce matrix materials of glass or other ceramic, and that the metalcoating provides a ductile bond between the glass of the fibers and theceramic of the matrix. When the fibers are generally parallellyoriented, the metal coating prevents crack propagation in the matrixfrom being transferred through the composites. Any suitable type ofglass fibers can be used even though they soften somewhat at theelevated temperatures, and any type of metal coating can be used whichwill withstand the firing conditions provided that the metal has amelting point above the softening point of the matrix glass. Suitableexamples of the metals, and alloys thereof, which can be used are;aluminum, copper, nickel, lead, zinc, tin, magnesium, indium, cadmium,antimony, bismuth, titanium, chromium, molybdenum, zirconium, and iron.The metal can be applied to the fibers from a molten condition providedthat the molten metal is solidified quickly and does not remain incontact with the glass fibers or matrix for more than the time that ittakes the metal to flow around the fibers, as demonstrated above, or canbe applied in any other suitable manner; as for'example by vapordeposition, as shown by U.S. Pat. No. 3,019,515; by a chemical coatingprocess, as shown for example in US. Pat. No. 2,900,274; or from a metalemulsion as described in US. Pat. No. 2,886,479. The amount of metalcoating that is necessary on the fibers will vary depending upon thereactivity of the metal with the matrix and/or glass fibers, and in mostinstances .the metal coating will perform its function of providingnecessary separation between the fiber and the matrix when its thicknessis more than approximately 0.00005 inch. Thicknesses of more thanapproximately 0.001 inch are not necessary in most instances, and mayunnecessarily increase the metal loading of the composite.

In general, glasses having a silica content of more than approximately50 percent have high tensile strength and generally high meltingtemperatures and are, therefore, ideally suited for making metal coatedglass fiber, glass and/or ceramic composites. Suitable examples include:glasses known in the trade as S- Glass," E-Glass," Pyrex, Pyroceram, andVycor. S-Glass has the general composition in percent by weight: 65% SiO25% A1 0 and MgO; and E-Glass has the following composition in percentby weight; 53% SiO 14.8% A1 0 16.8% CaO, 4.4% MgO, 9.5% B 0 andmiscellaneous non-essential oxides, as for example F TiO ,Na O, and Fe OPyrex has the following general composition in percent by weight: 80.5%SiO 0.20% Na O, 2.0% A1 0 and 12.9% B 0 Pyroceram has the followinggeneral composition in percent by weight: 70.7% SiO 0.20% Na O, 17.8% A10 1.4% ZnO, 4.18% TiO 3.15% MgO, and 2.38% Li O. Vycor has the followinggeneral composition in percent by weight: 96.3% SiO 04% A1 0 and 2.9% B0 A matrix glass which devitrifies, such as the Pyroceram, or the leadoxide glass given above and containing 83.0% PbO, has the advantage thatit can be heated at elevated temperatures to devitrify and produce aglass fiber reinforced ceramic. Metal coated quartz, S-Glass or E-Glassfibers are particularly useful for reinforcing such devitrifiablematerials. Further advantages can be had by sheathing metal coated glassfibers with devitrifiable glass, as for example the lead glass givenabove, followed by bonding the sheathing together to produce acomposite, and devitrifying the sheathing. Still further advantages ofthe invention can be had by incorporating the abrasive grit materialbetween the metal coated glass fiber reindistributing a grit and a glasspowder between glass.

sheathed metal fibers and fusing the powdered glass around the grit andto the sheathing.

Either the fibers or the matrix material, or both may be devitrified toincrease the temperature resistance and modulus of the composite. Byproper selection of the composition of the fiber or matrix materialfollowed by proper treatment such as heating, the fiber or matrix can bedevitrified.

The reinforcing effect which is achieved by the fibers is generallyproportional to the amount of fibers used, and can be as high as 70percent by volume, but will usually be more than 20 and preferably morethan 40 percent.

Composites having a fiber loading of from 20 to 70 percent by volumehave the improved properties of the present invention, in that they aregenerally shatter resistant, and can be deformed without catastrophicfailure. Less than 20 percent of the fibers can be used if permanentdeformation properties are not desired. Glass matrix compositions whichare devitrifiable, usually have their properties further improved by thedevitrification process and are, therefore, ideally suited for manyapplications.

I claim:

l. A strong light-weight composite useful at elevated temperatures andexhibiting apparent ductility comprising: generally parallel glassfibers having a silica content of at least approximately 50 percent byweight, a uniform sheathing of a thickness between 0.00005 and 0.001inch of a metal from the group consisting of aluminum, copper, nickel,lead, zinc, tin, magnesium, indium, cadmium, antimony, bismuth,titanium, chromium, molybdenum, zirconium, and iron around theindividual fibers, said sheathed fibers being bonded together in a glassmatrix by a matrix glass of a composition different from that of saidfibers and which has a softening point below the melting point of themetal sheathing, said matrix glass being fused to the metal sheathing onthe fibers, the glass fibers and metal sheathing occupying fromapproximately 20 to approx imately 70 percent by volume of thecomposite, and said sheathing effectively isolating the glass of saidfibers from said matrix glass to provide a glass composite that isdeformable and shatter resistant.

2. A composite of claim 1 wherein the glass fibers have a silica contentof above approximately 50 percent.

3. The composite of claim 1 wherein the metal sheathed fibers comprisefrom approximately 20 to approximately 70 percent by volume of thecomposite.

4. The composite of claim 1 wherein the matrix glass is devitrified.

5. The composite of claim 1 wherein the fibers are silica fibers.

SiO; 4.0

-Continued 7 A1 3.0 P 0 1 0.0 PbO 8 3.0

SiO 28.7

Na O

BaO

ZnO

1. A STRONG LIGHT-WEIGHT COMPOSITE USEFUL AT ELEVATED TEMPERATURES ANDEXHIBITING APPARENT DUCTILITY COMPRISING: GENERALLY PARALLEL GLASSFIBERS HAVING A SILICA CONTENT OF AT LEAST APPROXIMATELY 50 PERCENT BYWEIGHT, A UNIFORM SHEATHING OF A THICKNESS BETWEEN 0.00005 AND 0.001INCH OF A METAL FROM THE GROUP CONSISTING OF ALUMINUM, COPPER, NICKEL,LEAD, ZINC, TIN, MAGNESIUM, INDIUM, CADMIUM, ANTIMONY, BISMUTH,TITANIUM, CHROMIUM, MOLYBDENUM, ZIRCONIUM, AND IRON AROUND THEINDIVIDUAL FIBERS, SAID SHEATHED FIBERS BEING BONDED TOGETHER IN A GLASSMATRIX BY A MATRIX GLASS OF A COMPOSITION DIFFERENT FROM THAT OF SAIDFIBERS AND WHICH HAS A SOFTENING POINT BELOW THE MELTING POINT OF THEMETAL SHEATHING, SAID MATRIX GLASS BEING FUSED TO THE METAL SHEATHING ONTHE FIBERS, THE GLASS FIBERS AND METAL SHEATHING OCCUPYING FROMAPPROXIMATELY 20 TO APPROXIMATELY 70 PERCENT BY VOLUME OF THE COMPOSITE,AND SAID SHEATHING EFFECTIVELY ISOLATING THE GLASS OF SAID FIBERS FROMSAID MATRIX GLASS TO PROVIDE A GLASS COMPOSITE THAT IS DEFORMABLE ANDSHATTER RESISTANT.
 2. A composite of claim 1 wherein the glass fibershave a silica content of above approximately 50 percent.
 3. Thecomposite of claim 1 wherein the metal sheathed fibers comprise fromapproximately 20 to approximately 70 percent by volume of the composite.4. The composite of claim 1 wherein the matrix glass is devitrified. 5.The composite of claim 1 wherein the fibers are silica fibers.
 6. Thecomposite of claim 1 wherein the fibers are E-glass fibers.
 7. Thecomposite of claim 1 wherein the fibers are magnesium alumino-silicatefibers.
 8. The composite of claim 1 wherein the matrix glass hsa thefollowing approximate composition in parts by weight:
 9. The compositeof claim 1 wherein the matrix glass has the following approximatecomposition in percent by weight: